IF this doctrine does get taught, then it will have always been true. It will simply be a deepening of the interpretation of dogma that has existed since the time of Christ.
IF it does not, then the understanding at least so far as has been expressed to this date is simply not a correct understanding. That does not however mean that Mary is not in some way a co-Redeemer but only that in whatever way she is, it is not in the way that these petitioners think she is.
Also you have to understand that Catholic use of words and terms is much more precise and ‘unchanging’ than Protestant use of terms. Most (not all) Protestants, for example, now use the word “pray” only in the sense of ‘prayer to GOD ALONE’ --but that is not the historical use of the word nor is it the way the word was used in centuries past.
Today the word ‘co’ implies a equality.
Historically speaking, the word (with its roots in Latin ‘com’) simply meant ‘with’. Thus you would speak of a co-leader, for example. This person would act with the leader but was SUBORDINATE to the leader. He would only be able to act without the leader in the case of emergency. If the leader were somehow incapacitated, the co-leader could then lead.
Now Mary was not actually a ‘co-leader’ but she certainly, using the correct understanding of ‘co-Redeemer’ “CO-operated” in the redemption of mankind through her ‘fiat’ or acceptance of God’s word and becoming the mother of Christ. That cooperation was necessary to Christ’s birth. Mary of course did not herself ‘redeem’ us in any way, and Catholics have never taught that she did. But in her acceptance of God’s will she did indeed contribute, by bearing the Christ, to Christ’s redemption–that redemption however being entirely His, of His own power and no one else’s. Mary’s fiat made the birth of Christ possible. Christ’s sacrifice then made our redemption possible.
I fail to see how any of the above is ‘dicey’ theology.